Concurrent administration of bacteriostatic antibiotics (e.g., erythromycin, tetracycline) may diminish the
bactericidal effects of penicillins by slowing the rate of bacterial growth. Bactericidal agents work most
effectively against the immature cell wall of rapidly proliferating microorganisms. This has been demonstrated in
vitro; however, the clinical significance of this interaction is not well documented. There are few clinical
situations in which the concurrent use of static and cidal antibiotics are indicated. However, in selected
circumstances in which such therapy is appropriate, using adequate doses of antibacterial agents and beginning
penicillin therapy first, should minimize the potential for interaction.
Penicillin blood levels may be prolonged by concurrent administration of probenecid which blocks the renal tubular
secretion of penicillins.
Displacement of penicillin from plasma protein binding sites will elevate the level of free penicillin in the